Control device for electric motors



Nov. 9, 1943. c. .1. WERNER CONTROL DEVICE FOR ELECTRIC MOTORS Filed Nov. 12, 1941 onuno Patented Nov. 9, 1943 I I I 2,333,906 I CONTROL Device FOB ELECTRIC MOTORS Calvin J. Werner, Dayton, Ohio, assignor, to General Motors Corporation, Detroit, Mich., a corporation of Delaware Application November 12, 1941, Serial No. 418,743

3 Claims;

This invention relates to improvements in controls for electric motors. v

The device of the present invention is an improvement over the control devices disclosed in my Patent No. 2,095,579 of October 12, 1937. This patented device comprises a switch provided with counteracting spring and thermal elements adapted to control both the starting and running windings of the electric motor inaccordance with motor conditions.

Normally this device closes both winding circuits inasmuch as thethermal element normally overcomes the effect of the spring to actuate the device to circuit open position. At starting a heavy surge of current traverses the thermal element, which heats up and expands predeter- I minately as a resultofthe said heavy surge of current flow through, .it for a predetermined length of time, thereby permitting the spring to actuate the device to break the starting winding circuit. The motor now operates with its running winding circuit complete. As long as the'current of a normally running motor traverses the thermal element it will not be heated sufficiently to cause it to expand and permit the spring to open the running winding circuit. However, if the motor is stalled or subjected to an overload, the consequent excessive flow of current throughthe running winding circuit and the thermalfelement will cause a further heating up and thus an additional expansion of said element which again permits the spring to become effective to actuate the device, this time breaking the running winding circuit of the motor. I I I I From this it may be seen that the patented device provides starting control and overload protection to the motor.

As mentionedabove the thermal element of the patented device is so designed that a predetermined heavy surge of current must traverse said thermal element a predeterminedtime before it will heat up and expand sufficiently to permit the spring to effect opening of the motor startcircuit. This predetermined time is ofsufficient duration to permit the motor to. attain proper operating speed even when subjected to a heavy load condition, such load condition, however, being under the overload limit.

When the motor is subjected to comparatively light loads, it'will often attain proper running speed in a very short time, in fact, before the thermal element has become, sufficiently heated as to expandan'd permit opening of the starting circuitby the spring. Under these conditions the starting winding-circuit of the motor is maintained effective even while the motor is running at proper speed to perform its work. To permit the starting circuit to be closed and effective while the motor is running at proper working speed tends toward the production of undesirable noises in the motor such as growling or the like. i

- It is the object of the present invention to improve the patented device in such a way that said device will not only. function in the manner disclosed in the patent and generally defined above, but will also be adapted to render the starting winding circuit of the electric motor completely inefiective as soon as the motor reaches its proper working speed which, under somecircumstances, is before the time thethermal element of the device becomes effective to do the same thing.

This object is attained by providing a control device as described heretofore, with an electromagnetically controlled member adapted to be preconditioned by the said heavy surge of current flow during the motor starting cycle, said member being released to effect opening of the starting winding circuit when the said current flow drops off to normal, which occurs as soon as the motor is running properly to take care of its work. vAs has been said before, when the motor load is comparatively light, the motor will attain its proper running speed before the thermal element of the control device can become effective to open the starting circuit, thus this electromagnetically controlled member may become effective before the thermal element to open the starting circuit of the motor.

It will, of course, be understood that the electromagnetically controlled member would be ineffective to perform its function when the motor issubjected to heavier loads. under which circumstances running speed of the motor is generally not attained before the thermal element has become sufllciently heated to expand and permit the spring to effect starting circuit opening. If such running speed is not reached until the thermal element is predeterminately heated, current drop will not become effective to release the electromagnetically controlled member to perform its function of breaking the starting circuit until substantially the movement of circuit opening under control of the thermal ele itself unable to open the starting circuit until some other element of the device, such as the thermal element, broke its circuit.

Therefore it will readily be seen that although both the electromagnetically controlled member and the thermal element separately act to actuate the device to open the motor starting circuit, the first will perform this function before the other under certain circumstances to prevent undue noises while theother will perform the function under circumstances in which the first would not act at all.

invention will be apparent from the following description, reference being had to the accompanying drawing wherein a preferred embodiment of the present invention is clearly shown.

In the drawing: 7

All of the three figures are diagrammatic views showing the control device of tion connected with an electric motor.

Fig. 1 shows the device in the normal off position.

Fig; 2 shows the device in theoocked position immediately after the motor circuits have been connected with the source of electrical energy and, 3

3 shows the device after the motor has reached proper operating speed at which time thedevice has opened the stationary circuit of the motor.

Referring to the drawing the electric motor is designated as a' whol e by the numeral-2!. The starting winding of the motor is designated" by the numeral 2|,the running winding by the n ume'ral 22. Both windings lland 22 have one end connected to a com-morn terminal which in turn is connected with the switch terminal 24 thru a wire 25. The otherend of the starting winding 2| is connected with the stationary contact 25 of the switch thru wire 21. The other end of the running winding 22bit connected with one end of the electromagnet winding" 28 thru the wire 28. The opposite end of the electromagn'et 20 is connected with the stationa-rycontact 30 of the switch by a wire 3!.

notchll provided in" a face of" the switch body 36. This tongue isadapted'when on one side of the blade 38 to urge: the blade in one; direction and when on the Opposite side of" the blade to urge-the blade in the opposite-directioni' In the Fig; 1: themsting' point oithe tongue "in the notch or the budyv portion.- ofs'the switchis to the left of the: fiexibllr. blade; 3% and: tly tongue. ll, will urge, the blade 38 to; the: right" so as to cause engagementof contact. 39= with the stationary contact 30. 3

Another. flexible contact blade has one end attached to the. body 35, of the switch as 213 33 andcarrlesacontact 5i. adjacentitsfree end so as to. cooperate. and engage with. the. stationary contact 26.- A.-tongue 52,. similar to'tongue .40 of .,the blade 38,.

body, and. in. the. position shown in Fig. l tongue. 52 urges blade. ilf'so that itS cOnt-at'5l engages the contact 25. To cause contact disengagement it is necessary'mere'ly to rotate the body 36' the present inven-' The; switch, designoted as a whole by thenumeral 35, comprises has its: freeend. resting in. the notch 53 of. the switch of the switch clockwise about 3 the pivot point 31 from the position shown in Fig. 1, in which case the resting point of tongue 52 in its notch 53 will pass from the left to the right side of flexible contact blade 50 so that said tongue will urge the blade 50 to the left causing its contact 5! to be moved out of engagement with its stationary contact 26 following which, upon continued clockwise movement of the switch body 36 the restingpoint of tongue in its notch 4| will pass from the left to the right y side of the flexible blade 38 urging it toward the Further objects and advantages of the present left to break engagement of its contact 39 with the cooperating stationary contacts 3!). It will be noted in Fig. 1. that the resting point of tongue 52 in its notch 53 is closer to alignment with its flexible blade than the resting point of blade 40 in its notch 4| to the flexible blade 38, thus clockwise rotation of the switch body 36 will result'in successive movements of blades 50 and 38, the blade 50 first being shifted to open its contact engagement following which the blade 38 will be moved to disenga e its contact 39 from contact 30.

The means for moving the switch body 36 about its pivot point 31 comprises counteracting elements one, a spring with one end anchored to a stationary post 61 the other to an ear 32 formed on the switch body 36' adjacent its pivot point. The otherelement comprises a thermoelectric strut GI having one end anchored to and electrically connected with an ear 6!! provided on the switch body 36; the other end of said strut being secured toa stationary terminal block 66. The strut 64 is so adjusted thatnormally it holds the switch body 38 in the contact closing position as shown in I overcoming the effort of the spring 6t" tdmcvetheswrtch body clockwise. However, the thermoelectric strut is oi" such a character that in responseto a predetermined current flow therethru it will expand thus permitting the spring to become effective to rotate the switch bcdy 38 clockwise in accordance with the deg-reeof expansion" ofthe strut 8t.

' It has been stated that the present invention relates to an improvement over the switch disclosed in applicants previously referred to Patent' #2-,095;579. This nnprovementincludes the addition oi. an electromagnetically operated device comprising an electromagnet having a core 78 about which is provided the electromagnet winding 28. An armature T l pivoted on the member 121s adapted'to be actuated clockwise as regards Fig; 1' by energization of the electromagnet. A spring 13 interposed between armature and an abutment block 14 urgesthe armature counterclockwise away from the electromagnet core" 19" the end of the armature opposite the core havingv an insulated portion which engages a hooked portion 56' provided on the free end for the flexible contact blade 30 as shown in Fig. l.

From the aforegoing' it will be seenv that-the tongue 52 of the spring blade 50 urges said spring blade to the right to cause engagement of contact 5| with the stationary contact 26 while spring" exerts pressure upon the armature H engaging the hooked portion 36 of the flexible bladefiflt'ending to' move it in the opposite direction to cause. disengagement of the. contact 51 with the contact 26'; However tongue 52' and spring" are so designedthattheefiort'of'tongue 52 to move the blade 5l1into contact engaging position is' slightly greater than the effort of the spring 13 upon thearmature Tl tending. to move said fiexibiebladeinto the contact disenone flowing thru gaging position so' thatlnormally contact will be held in engagementwith its cooperating stationary contact. 26, even. against the counteracting effort of said'spring 13.

The anchor :block 68 towhich, one end of thermo electric strut 64 issecured is connected thru wirey61 with switch terminal 68. Switch in Fig. 2 for purpose of operating the motor, an

initial heavy surge of current will traverse the following circuits. From the power line 8| across switch 82 to thermoelectric strut 64 to the body 38 of the switch, from here two circuits are established, the flexible contact blade 38 attached to the switch body36, thru contacts 38 and 30, thru wire 3|, electromagnet winding 28, wire 28, running winding 22 of the motor to terminal 23, thencethru wire terminal 24 of switch 82 to the otherside 80 of the power line. The second circuit fromthe thermoelectric strut G4 and body 36 will flow thru the flexible contact blade across contacts 5| and 26 thru wire 21 starting winding 2| of. motor 2|], to the common terminal 23, thence to the other side 80 of the power line through wire 25 and switch 82. This initial heavy surge of current flow will start the motor to operate and will, at the same time energize the electromagnet winding 28 and its core 18 to attract the armature 1|, moving it clockwise about its pivotal point 12 and thereby moving its insulated end out of. engagement and in spaced relation with the hookedend 5,5 of the flexible contact. blade 50. This is clearly shown in the Fig. 2. This current flowing thru the. thermoelectric strut 84 will cause it to be heated resulting in an expansion thereof.

In the preamble to this specification it has been stated that the thermo element or strut 64 is so designed that a predetermined heavy surge of current must traverse it a predetermined time before it will heat up and expand sufliciently to permit spring 68. to effect opening of the motor starting circuit; Thatthis predetermined time isv of sufficient duration to permit the motor to attain proper operating speed even when subjected to a heavy load condition; such load condition however, being under the overload limit. v Q

It has also been previously stated that when a motor is subjected to a comparatively light' load it will often attain properrunning speed in a very short time, in fact, before the thermoelectric element 84 has been sufficiently heated as to expand and permit openin'g'of thestarting circuit by the spring. That under such conditions maintenance of the starting circuit while the motor'is running at the proper speed to'perform its work results in the production of undesirablenoises such as growling by the motor or v the like. i ,i

Thus, in the present invention and thru the provisions of the electromagnetically operated device the starting circuit may be opened when and as soon as the motor begins to operate at proper speed. When this occurs, that is, as soon as the motor attains the initial heavy surge of starting current will drop or be decreased such decrease in the flow of current partially de-energizing the electromagnet comprising winding 28 and core 10.

the terminal 6 8,thence thru the wire 61 to the abutment block 66, thru the proper operating speed Upon .partial de-energization of said electro- ;magnet spring 13 acting upon the arm 1| will now be of sufiicient strength to move the armature 1| quicklyfrom the position shown in the Fig. 2 to the attracted position shown in the Fig. 3 toward its normal position shown in Fig. 1, such quick shifting of the armature exerting a hammer I blow effect upon the hooked end of the flexible contact blade'50 and overcomming the efiort of tongue 52 to hold said blade 50 in its contact engaging position. When the released armature has effected movement of the blade 50 as shown in Fig. 3 due to the drop in the current flow thru the electromagnet and the resultant partial de-energization thereof, contact 5| is separated from its cooperating stationary contact 2t and thus the circuit including the starting winding 2| is completely interrupted thereby rendering said starting winding 2|. entirely in-.- effective. Now only the running winding completed across closed contacts 39 and 3|) is being energized for normal motor operatiom If for some reason such as a heavy load on the motor prevents or more specifically postpones the aforedescribed drop in the current flow thru the motor circuits then the electromagnet will not be partially de-energized but will be sufficiently energized to maintain the armature 1| in attracted positionas shown in Fig 2. As a consequence the starting winding circuit across contacts 5| and 56 will be maintained as longas sucha drop in current does not occur, and under some motor load conditions the electromagnetic device might not function at all, the opening of the starting winding circuit being effected only after the current has traversed the thermoelectric strutiil sufiiciently to expand said strut to permit spring 68 to become efiective and operate the switch body 35 to open contacts 5| and 26. Thus it may be seen that not only are tion incase the other control means berendered ineffective, for one reason or another. I I

From the aforegoing description it may readily be seen that in the present invention applicant has provided a control device for an 'electric motor which not only protects the motor against damage under abnormal running conditionspbut it also provides a dual means for controlling the starting circuit of said motor. Said starting circuit is rendered ineffective by one portion of, the device as soon as themotor becomes operative thereby avoiding undesirable noises in the motor and is also interrupted and rendered completely ineffective by another portion of the device in response to an excessive device or a current flow of predetermined value I and duration.

While the form of embodiment of the present invention as herein disclosed constitutes apreto' be understood that other forms might be'ado'pted, all coming within the scope of the claims which follow.

What is claimed is as follows:

l. A control device for an electric motor having starting and running winding circuits adapted to be connected to a source of electric power; a

switch having a separate pair of normally closed contacts electrically connected in each motor circuit; thermo-electric means secured to the switch and electrically connected in both motor circuits said thermo-electric means being adaptcurrent flow thru" the ed t: be energized and rendered active to .cife'ct motion oi-the contacts in thestarting winding circuit in response to either an excessive current or a normal current flow oi predetermined duration therethrovsh; and electromagnetic means comprising a winding electrically conmeted in series with th running winding circuit and an armature mechanically engaging one of the contacts in the starting winding circuit,. said electromagnetic meansbcing: rendered effective by a predetermined drop in the flow 01 current therethrough to' separate said contacts in the starting winding circuit.

2 A control device for an electric motor having starting and running winding circuits adapted to" be connected to a source of electric power; a 'mtcn having a'separste pair of normally closed contacts electrically connected in each motor circuit: theme-electric means secured to the switch and electrically connected in both motor circuits, said theme-electric means being adapted to be energized and rendered active by either an excessi've current dowor a current flow of predetere mined duration therethrough for efiecting operation of the switch to open the starting winding circuit of the motor regardless of motor opera- Lion; and electromagnetic means supported by the switch and connected in series with the running winding circuit,- said electromagnetic means being rendered cii'ectivc, when its energization is reduced by a predetermined drop in current flow thcrethrough resulting from the motor attaining voperating speed, for engaging and opening the pair of contacts in the starting winding circuit.

3. A control device for an electric motor having astarting and a running winding adapted to be connected to a source of electric power; a switch provided with a set of normally closed contacts connected in circuit with each motor winding;

resilient means yieldably urging the switch to open lts contacts; a thermal member mechanically securedto the switch and connected in series circuit with both motor windings respecmay. said thermal member being normally tensioned to hold the switch in contact closing position against the opposing effect of the resilient means and being adapted to be heated by either an excessive current flow or a current flow of predetermined duration therethrough and expand, whereby the resilient means is rendered eflective .tomove the switch and open its contacts; and an electromagnetic device connected in series with .therunoing winding, and energized by the closin of its circuit to be moved into operative position said device being adapted to strike and open the contacts in the starting winding circuit when it is released in response to reduced energization due to a predetermined drop in current flow through said device resulting from the motor.at-

taining operating speed. 7

4. A control device for an electric motor having starting and running windings adapted to be connected to a source of electric power; a switch Providing a separate set ,of normally closed contacts in series with each motor winding and a thermo-electric member connected in series with the starting and the circuit for opening the contacts each motor windinguand attached to the switch so as to eflect its operatim to open the sets of contacts in response to either an excessive current flow or a current flow of predetermined duration therethrough; and an electromagnetic device connected in circuit with the running winding, and adapted to be preconditioned by the initial surge of current through its circuit,- as the motor windings are energizcd'for motor starting purposes, for engaging and opening the contacts in circuit with the starting winding in response to a predetermined drop in current flow resulting from the motor attaining proper operating speed. 5. A control device for an electric motor having starting and running windings adapted to be connected to a source of electric power; a switch having a separate set of normally closed contacts connected in series with each motor winding; 9,

spring attached to the switch and yleldably urging the switch to open its contacts; thermo-electric means secured to the switch and electrically connected to both motor windings, said means being normally tensioneci to hold the switch in contact closing position against the efiect oi the spring and being adapted to be heated and consequently expanded in response to either an excessive or a normal current flow of predetermined duration therethrough for effecting operation of the switch by the spring to open the contacts; and an electromagnetic device comprising a magnet winding connected in series with the running winding and an annature normally engaging one or the contacts in series-with the starting winding, said device beingenergized -by the closing of the running winding circuit to move the armature out of its contact engagement, said armature being quickly returned to its normal position and in so doing separating the contact in series with the starting winding in response to a predetermined drop in current flow therethrough resulting from the motor attaining proper operating speed. I

6. A control device for an electric motor having starting and running windings adapted to be connected to a source of electric power; a switch providing a separate set of normally closed contacts connected in circuit with each motor winding; and a plurality of switch control means, one a thermo-electric member attached to the switch and connected in series with both motor windings and adapted to efiect operation of the switch successively to open the contacts in circuit with running windings, respecin response to predetermined current flowthrough saidmember, the other switch-control means comprising an electromagnetic device, connected in series with the running winding of the motor and normally engaging a contact in circuit with the starting winding; said device being preconditioned by the completion of its in circuit with the starting winding when the current flow through the electromagnetic device and running winding drops to a predetermined value CALVIN J; WERNER. 

